In many communication, entertainment and surveillance industries a very selective electro acoustic pickup of distant sound on a highly unidirectional basis while also substantially rejecting all other sounds from all other directions is needed.
Two main types of microphones attempt to obtain the above mentioned requirements and are commonly used in the above mentioned industries. These are the transmission line and the parabolic reflector. Both of these microphones are actually a form of enhancing the pickup pattern of a cardiod, hypercardiod, or some other public domain basic microphone design concept.
In the transmission line designs sound coming from directions other than the one desired are not completely cancelled but are received from many various smaller side and or rear lobes. Reception of undesired sound through side or rear lobes not only effects the overall directivity of the device, but in most cases effects the low frequency to high frequency ratio of these extraneous sounds, making these sounds spectrally distorted. Each side and or rear lobe having a somewhat different frequency response and a zone of very low sensitivity between the adjacent side lobes and cause large unwanted changes in the undesired sound recepted, when the microphone is moved to follow a moving sound source.
In the parabolic reflector type of microphone, the ability of directivity is directly proportional to the size of the reflector. In most cases, a reflector large enough to have a good directivity in the low frequency audio range will be so physically large as to make its use limited. Smaller more portable reflectors generally have insufficient low frequency response to be used in wide frequency response audio applications.
No known prior art unidirectional microphone design can produce maximum rejection of recepted sound from the rear of the microphone and the sides of the microphone and all angles inbetween the rear and sides of the microphone in a uniform fashion over a wide frequency band.